Download - Catalyst Project ID: PM028 Characterization
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Catalyst Characterization
Thomas Watkins, Larry Allard, Michael Lance and Harry Meyer; ORNL
Krishna Kamasamudram and Alex Yezerets; Cummins Inc.
Sponsored byU.S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies Program
Project ID: PM028
2010 DOE Vehicle Technologies Annual Merit Review and Peer Evaluation Meeting
June 10, 2010
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Background: Exhaust Aftertreatment
• Ammonia containing compounds added to diesel exhaust to reduce NOx to N2.
– e.g., NH3 + NO + 1/4O2 ⇒ N2 + 3/2H2O– Excess ammonia is often needed resulting in NH3 escaping or “slip”– This ammonia must be removed by a secondary step.
• NH3 slip is currently not regulated in US, however for sociability and environmental reasons, Cummins chose to use Ammonia Oxidation (AMOX) Catalyst* device to ensure that ammonia slip to ambient is minimal
• An AMOX catalyst can be used to convert the NH3 slip to N2+ H2O
– Candidate catalysts: zeolite-based and alumina-supported metal or metal oxide catalysts
– Temperature and water content play a big role in the functioning and aging of these catalysts
* Also called Selective catalytic oxidation (SCO) or Ammonia Slip catalyst (ASC)
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Overview
DOE 2009 Vehicle Technologies Annual Merit Review and Peer Evaluation Meeting
Timeline
• Start: June 2002
• End: Sept. 2012
• 78% complete
Budget
• Total Project funding– DOE-$2.2M– Contractor-$2.3M
• Funding received:– FY09 $196k– FY10 $147k
Barriers*- Advanced Combustion Engine Research: Emission
Control System
• Poor durability materials degradation/aging
• Numerous components
• Costly precious metal content
Partners
• Cummins Inc.• Johnson Matthey
* FreedomCar and Vehicle Technologies Program, Multi-Year Program Plan 2006-2011, Sept 2006, pp. 3.4-10, 21.
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Objective
• The purpose of this effort is to produce a quantitative understanding of the process/product interdependence leading to catalyst systems with improved final product quality, resulting in diesel emission levels that meet the prevailing emission requirements.
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Milestones
• Milestone09: Complete evaluation of feasibility of the advanced tools available at ORNL for quantitative analysis of the materials changes underlying the selective catalytic reduction catalyst performance degradation with age.
• Milestone10: Initiate evaluation of feasibility of the advanced tools available at ORNL for quantitative analysis of the materials changes underlying the AMOX catalyst performance degradation with age.
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1 Approach: Technical
• Focus on AMOX materials with the practically-relevant properties
• Experimentally characterize materials, supplied by Cummins, from all stages of the catalyst’s lifecycle: fresh, de-greened, aged, regenerated, on-engine and off-engine, etc.
• Determinations include: crystal structure, morphology, phase distribution, particle size and surface species of catalytically active materials.
• Seek the atomic mechanisms and chemistry of adsorption and regeneration processes
• Seek to understand the thermal and hydrothermal aging processes and other degradation mechanisms throughout the lifecycle of the catalytic material.
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2 Approach: Relevance to barriers & Integration• Impact on barriers: Experimental determination…
– Of why, when, where and extent of hydrothermal aging degradation on the material system’s performance. Understanding mechanisms allows new engine strategies to mitigate aging. Also, better catalysts can be designed.
– Input for design for fewer, multi-functional components
– Improved strategies minimize functional loss, save precious metals
• Integration within Vehicle Technology program:– Utilizes characterization tools acquired and maintained
by the High Temperature Materials Laboratory (HTML) Program
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3 Approach: Relevance to Vehicle Technologies Goals• Improve commercial vehicle engine
efficiency at least 20%– With an efficient and durable AMOX, higher NOx
conversion efficiencies can be attained, thus minimizing constrains on engine-out NOx emissions and allowing engines to be tuned for optimal fuel efficiency, cost and durability
• Achieve engine system cost, durability and emissions targets– See above
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X-Ray Diffraction: AMOX catalyst is a Zeolite on a cordierite substrate
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500.0µm
END_2
500.0µm
Mid
500.0µm
End_1
X-ray Photoelectron Spectroscopy: Split core layout inside sample chamber
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020040060080010001200Binding Energy (eV)
Fe
O
C
Si
Al
End_1
Mid
End_2
X-ray Photoelectron Spectroscopy: shows composition and valence at the 3 locations of as-received AMOX sample
Surface Composition (at.%)Fe Al Si O C
End_1 3.7 12.4 21.7 60.9 1.4Mid 3.8 12.2 22.3 60.7 1.0End_2 3.9 12.7 21.4 59.7 2.4Avg. 3.8 12.4 21.8 60.4 1.6
Si/Fe = 5.8Si/Al = 1.8
5 regions of interest in the spectra
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710720730Binding Energy (eV)
Satellite structure at ~718 eV from Fe3+.
Fe 2p3/2BE~711 eV
Al:Si:Fe• Assume Al2O3, SiO2, and Fe2O3• Ignoring the adsorbed water O 1s signal, metal/oxygen ratio 0.68 (otherwise 0.59), indicating a slight oxygen deficiency in the near surface region
X-ray Photoelectron Spectroscopy: Fe 2P core level spectra are identical for all 3 sample regions; indicate Fe3+
• AMOX zeolite shows significantly higher Fe conc. than former SCR samples• Facilitate detection and characterization of the Fe species by TEM techniques.
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7173757779Binding Energy (eV)
99101103105107Binding Energy (eV)
Si 2p
Al 2p
526530534538Binding Energy (eV)
O 1s
O 1s spectrum•Al-O/Si-O bond (~532 eV)•Fe-O bonding (~530 eV)•adsorbed water/-OH (~534 eV).
End_1
End_2
Mid
End_1
End_2
Mid
X-ray Photoelectron Spectroscopy: Si 2P, Al 2p & O 1s core level spectra also identical for all 3 sample regions; consistent with literature for zeolites
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Fourier Transform Infrared Spectrum of as-received Fe-Zeolite/AMOX catalyst
0 500 1000 1500 2000 2500 3000 3500 4000
Frequency (cm-1)
Abs
orba
nce
(a.u
.)
Hydrocarbon Species
-OHNOx Species
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Collaborations and coordinations with other institutions
• Partners – Cummins Inc. (Industry): supplies samples; share experimental results
on samples (e.g. catalyst performance results during aging); exchange of technical information to assist with each others analyses; face to face meetings at least 2X/year
– Johnson Matthey (Industry): exchange of technical information
• Tech transfer– Provide guidance for system design, cost (reduce precious metal
content, and optimization.– Reduce materials and functionality margins for related to catalyst
aging.
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Future Work
• Continue ammonia oxidation (AMOX) catalyst characterization of a practically-relevant zeolite catalyst subjected to hydrothermal aging for lifetime prediction model input. Utilize new in-situ capabilities.
• Focus on understanding the catalyst degradation mechanisms due to hydrothermal aging using the tools developed under this CRADA (FY10).
• Assist Cummins to competitively produce engines which attain the required prevailing emission levels and beyond while maintaining the advantage of the diesel’s inherent energy efficiency (FY10 & FY11).
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Summary• Through 2009, progress has been slowed
considerably due to sample unavailability because of the 2010 product launch focus.
• Samples received in January 2010• X-Ray Diffraction, Transmission Electron Microscopy (TEM), Diffuse Reflectance Infra-
red Fourier Transform spectroscopy, Fourier Transform Infra-red spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy: will be applied to characterize the new AMOX samples.
• Special in-situ capabilities are in place:– FTIR: High Temperature Cell– TEM: E-cell reaction holder: heating + gas
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Summary (cont’d)• Special in-situ capabilities are in place:
– TEM: elemental mapping with new x-ray detector– TEM: Energy-loss electron spectroscopy for chemical
binding information– TEM: Our new capability for in-situ heating and gas
reaction studies may also be used as the study develops, to provide dynamic/kinetic information on the behavior of the catalyst under selected treatment conditions. Results will be compared to bench tests.
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Acronyms• ACEM = aberration-corrected electron microscope
• BF = bright-field
• DRIFTS = Diffuse reflectance infra-red Fourier transform spectroscopy
• EDS = Energy dispersive spectroscopy
• EPA = Environmental Protection Agency
• HA-ADF = high-angle annular dark-field
• NMR = Nuclear Magnetic Resonance
• NOx = Nitrogen and Oxygen containing compounds
• ORNL = Oak Ridge National Laboratory
• SCR = selective catalytic reduction
• STEM = Scanning Transmission Electron Microscopy
• XPS = X-ray photoelectron spectroscopy
• XRD = X-Ray Diffraction
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What is a zeolite?*
• Classical definition: a crystalline, porous aluminosilicate
• Current definition: porous oxide structures with well-defined pore structures and a high degree of crystallinity
• Large number of structures possible
• Pores/Channels-molecular sieves
* www.personal.utulsa.edu/~geoffrey-price/zeolite/zeo_narr.htm
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Chemical interactions of zeolites
• Si-O4 tetrahedra and (Al-O4)-1 tetrahedra– Charge compensation with cations in pores
• Uses:– Ion exchange as in water softeners– Cation=H+, becomes a strong acid-catalytically
active– Other metal cations-shape selective catalysis
* www.personal.utulsa.edu/~geoffrey-price/zeolite/zeo_narr.htm